Bearing shell and a radial plain bearing mounted in a bearing carrying body provided with a bearing cap

ABSTRACT

In order to take account of dimensional variations in crankcases and connecting rods, the lower bearing shell (9) in the unmounted state is formed such that the outer contour is in the shape of an arc having a radius r a  and the inner contour has the shape of a semi-ellipse having semi-axes a i  and b i . The bearing semi-axis a i  passes through the vertex (19) of the lower bearing shell (9). When the bearing is mounted, the contour of the upper bearing shell (8) remains unchanged while the lower bearing shell (9) is slightly deformed such that its outer contour assumes the shape of a semi-ellipse having semi-axes a a  and b a . The short semi-axis b a  passes through the vertex (19) of the lower bearing shell (9).

The invention relates to a bearing shell according to the preamble ofclaim 1. The invention also relates to a radial plain bearing mounted ina bearing-carrying body provided with a bearing cap, the bearingcomprising an upper bearing shell and a lower bearing shell for mountingin internal combustion engines, particularly for the mounting ofcrankshafts in crankcases and in connecting rods, which are exposed tobearing loading whose magnitude and direction change within a certaincycle, wherein the wall thickness of the lower bearing shell increasesfrom the vertex of the circumference to the joint faces and the innercontour has the shape of a circular arc with the radius r_(i).

Such radial plain bearings are used, for instance, in car engines,distinction being made between flange bearings, main bearings andconnecting rod bearing. The upper bearing shell is that bearing shellwhich is situated in a crankcase or in a connecting rod, while the lowerbearing shell is mounted in the crankcase cap and is screwed to theupper part. For such bearings are required service lives whichcorrespond to the service life of the car engine. In car engines whoseservice life is more than 100 000 km, the bearings must often bereplaced earlier.

Attempts have therefore been made to obtain, by suitable geometry of thebearing, improved lubrication and thereby longer service life.

From DE-OS 14 25 125 are known multi-shell bearings in which the wallthickness of every shell changes along its length, while the center ofthe inner diameter of each shell is situated eccentrically to the centerof the outer diameter of the shell, and the centre of the inner diameterof each shell lies on the bisector of the angle of the shellcircumference. In such bearings, which may be composed of two shellsonly, the surface of the bearing has not a cross-section in the shape ofa circular arc, because in all cases the inner diameters of the shellshave no common centre. Every bearing shell has therefore its own radiusof curvature which causes jumps in wall thickness at the joint faces. Ifthe wall thicknesses in the region of the joint faces are of the samesize, then both the shells of the multi-shell bearing have their maximumthickness in the vertex. In this way a kind of lemon-shaped bore isobtained.

A similar bearing, in which the centers are situated with equal spacingon both sides of the joint face in a radial plane which is twistedthrough an angle out of the plane of main loading, is known from DE-AS16 75 743.

From DE-OS 31 36 199 is known to provide the part of the bearing whichexhibits greater resistance to deformation with a bearing half-shell inthe shape of a circular arc, and the part of the bearing which exhibitsa smaller resistance to deformation with an oval bearing halfshell. Thebearing shell in the shape of a circular arc has a constant wallthickness, whereas the wall thickness of the oval bearing shelldecreases towards the joint faces, so that there is a jump in wallthickness in the region of the joint faces.

U.S. Pat. No. 4,311,349 describes a bearing set comprising two identicalbearing shells whose wall thicknesses are reduced in the region of jointfaces so that also here a kind of lemon-shaped bore is produced.

From U.S. Pat. No. 4,307,921 is known a bearing in which the wallthickness of the shells in the region of one joint face is greater thanin the region of the other joint face. The inner contour of the bearingshells is formed by two superimposed bearing bores with offset centers.

U.S. Pat. No. 4,488,826 describes an eccentric bearing bore in which theeccentrically arranged crank journal has on one side a small clearanceand on the other side a large clearance. The center of the eccentricbearing bore is displaced to the region of smaller loading, so that thelarger clearance provided there may be used for the supply of lubricant.The two bearing shells, which are identical, have in the region of onejoint face a greater wall thickness which continuously decreases in thecircumferential direction of the shell, so that it is smallest in theregion of the other joint face. Because a large clearance should beavailable in the region of small loading, the joint face does not extendperpendicularly to the longitudinal axis of the connecting rod, whichrequires an obliquely split connecting rod.

From DE-PS 698002 is known a split plain bearing in which the upperbearing shell is larger than the lower bearing shell, so that the twoends of the upper bearing shell, whose cross-sectional area decreasesand which project relative to the bearing-carrying body, provide goodcentering. To be able to have the corresponding bearing shell strongerin the region of the greatest loading, the whole inner diameter of boththe bearing shells is displaced towards the bearing cap eccentrically tothe common outer diameter of the two bearing shells which remainedunchanged, so that the lower bearing shell has in the region of thevertex a smaller wall thickness than in the region of its joint face.

It was found that no significant increase of the life could be achievedwith these known bearings.

The aim of the invention is to devise bearing shells and also a radialplane bearing which has such a long service life that it is probablethat it will not have to be changed during the service life of theinternal combustion engine.

The aim is achieved with a bearing shell having the features of claim 1.Claim 4 deals with a mounted radial plane bearing.

The bearing receiving bores in crankcases and connecting rods are soprovided that the center of the bearing receiving bore coincides withthe center of the crank journal of the crankshaft, while between thecrank journal and the associated bearing shell is provided a certainclearance. After provision of the bearing receiving bore the cap isscrewed off, the bearing shells are inserted and the cap is againscrewed on while observing tightening instructions.

The invention is based on the discovery that after the first removal andsubsequent screwing on, the cap undergoes a dimensional change, whilethe region of the bearing bore in the case remains largely unchanged. Itwas found that these dimensional changes are limited to the vertexregion of the cap and are dependent on the shape and the material of thecap. These dimensional changes amount up to 0.1 mm. The dimensionalchange, which will be hereinafter called dimensional variation of thecap, causes reduction of the clearance between the lower bearing shelland the crankshaft, which leads generally to higher loading of the lowerbearing shell and thereby to greater wear, which is ultimately thereason for premature breakdown of the bearing.

This dimensional variation of the cap is according to the inventiontaken into consideration by specially shaped bearing shells. It istherefore provided that the inner contour of the bearing shell which ismounted in the cap has the shape of a semi-ellipse with semi-axes a_(i)and b_(i), wherein the long semi-axis a_(i) passes through the vertex ofthe bearing shell.

Because bearing shells are composed of backing material and bearingmaterial, the geometry of the bearing shell is preferably formed bygiving the backing material of the bearing shell a constant thicknessalong the whole circumference while the bearing material, which isdeposited on the backing material, has a variable thickness. For outerdiameters of bearings of 20 mm to 1000 mm the difference in wallthickness between the vertex and the region of the joint faces ispreferably up to 0.1 mm. Because the dimensional variation of the cap isdependent on the material and shape of the cap, the difference in wallthickness must be adapted to these properties of the cap. For thispurpose must be, for instance, for every engine type first determinedthe relevant dimensional variation of the caps.

When such bearing shell is mounted in a crankcase as a lower bearingshell together with an upper bearing shell to provide a radial planebearing, it is, in view of the dimensional variation of the cap,slightly deformed such that the previously elliptical inner contourchanges into a contour in the shape of a circular arc, whilesimultaneously the outer contour changes from the shape of a circulararc into an elliptical shape. The outer contour of the lower bearingshell assumes the shape of a horizontally situated ellipse, which meansthat the short semi-axis b_(a) passes through the vertex of the lowerbearing shell and the long semi-axis a_(a) lies in the plane of thejoint faces.

The inner contours of the upper and lower bearing shells lie on a commoncircle, which corresponds to the circle that would be obtained with twoidentical bearing shells and without dimensional variation of the cap.In spite of the dimensional variation of the cap, the clearance neededbetween the bearing shell and the crank journal is fully preservedthanks to the geometry of the lower bearing shell which takes thisdimensional variation into consideration, so that there is no additionalwear as a consequence of the dimensional variation of the cap.

The lower bearing shell is preferably so shaped that the center of theouter diameter of the upper bearing shell and the center of the innerdiameter of the lower bearing shell coincide.

The upper bearing shell may have a constant thickness along the wholecircumference. It is also possible that a so-called lemon-shaped bore issuperimposed on the bearing bore, so that also the wall thickness of theupper bearing shell in the vertex is greater than in the region of thejoint faces.

The same applies also to caps screwed on to connecting rods. In allcases the bearing shells should preferably be mounted such that thejoint faces of the bearing shells lie in the splitting plane of the cap.

The wall thickness in the region of the joint faces of the upper andlower bearing shells is preferably identical to avoid jump in thicknessin the region of the joint faces.

Considerable increase in operational performance could be achievedwithout any problems in engines equipped with radial plane bearingsaccording to the invention.

The aforementioned objects, features and advantages of the inventionwill, in part, be pointed out with particularity and will, in part,become obvious from the following more detailed description of preferredembodiments of the invention, taken in conjunction with the accompanyingdiagrammatic drawings, which form an integral part thereof.

IN THE DRAWINGS

FIG. 1 shows the geometry of a bearing receiving bore,

FIG. 2 is a side elevation of an upper bearing shell and a lower bearingshell before mounting,

FIG. 3 is a side elevation of the upper bearing shell and the lowerbearing shell shown in FIG. 2 after mounting,

FIG. 4 is a front elevation of a-connecting rod with a crank journal insection,

FIG. 5 is a front elevation of a crankcase with a main journal insection, and

FIG. 6 is a side elevation of an upper bearing shell and a lower bearingshell with a lemon-shaped bore.

IN THE VARIOUS FIGURES OF THE DRAWING, LIKE REFERENCE CHARACTERSDESIGNATE LIKE PARTS OR DIMENSIONS.

FIG. 1 shows diagrammatically the geometry of a bearing receiving borein a connecting rod or a crankcase, in which L₁ describes the circularbearing receiving bore after the crankcase or connecting rod have beenmachined in a boring machine.

When the cap, which forms the lower half of the bearing receiving bore,is unscrewed and subsequently, after mounting of the bearing shells,attached again while observing the tightening instructions, the innercontour changes due to the dimensional variations of the cap. After themounting of the bearing, the bearing receiving bore is described by thecurve L₂, which has the shape of a horizontally extending ellipse. Thereduction of the diameter of the bearing receiving bore in the region ofthe vertex is caused by the dimensional variations D of the cap.

In FIG. 2 are shown two bearing shells 8, 9 in unmounted state. Theupper bearing shell 8 and also the lower bearing shell 9 comprisebacking material 22 on which is deposited bearing material 23. The upperbearing shell 8 has a constant wall thickness along the wholecircumference. The lower bearing shell 9 has in the vertex 19 a smallerwall thickness than in the region of the joint faces 11, where the wallthickness corresponds to that of the upper bearing shell 8. Thereduction of wall thickness in the region of the vertex is at theexpense of the bearing material 23, so that the backing material 22 hasa constant thickness along the whole circumference. The inner contour ofthe lower bearing shell has the shape of a standing semi-ellipse, whichmeans that the long semi-axis a_(i) passes through the vertex 19 of thelower bearing shell, while the short semi-axis b_(i) is situated in theplane of the joint faces 11 and equals the radius r_(i) of the innerdiameter of the upper bearing shell 8.

When the bearing shells 8, 9 are mounted in a crankcase, the shape ofthe upper bearing shell 8 remains unchanged but the lower bearing shell9 is slightly deformed due to the dimensional variations of the cap.Neither the case nor the cap are shown in FIG. 3. The dimensionalvariation of the cap causes in the region of the vertex 19 shortening ofthe long semi-axis a_(i) or of the radius r_(a) of the outer diameter ofthe lower bearing shell 9. This shortening causes that the previouslyelliptical inner contour of the lower bearing shell changes now to aninner contour in the shape of a circular arc and, as a consequence, thelong semi-axis a_(i) has now the value of the radius r_(i) of the innerdiameter of the upper bearing shell 8. Due to the different wallthickness of the lower bearing shell 9, the outer contour of the lowerbearing shell 9, which had previously the shape of a circular arc,changes simultaneously into the shape of a horizontally situated ellipsewhose short semi-axis b_(a) passes through the vertex 19 and whose longsemi-axis a_(a) is situated in the plane of the joint faces 11 and isequal to the radius r_(a) of the outer diameter of the upper bearingshell 8.

In FIG. 4 is shown a connecting rod 2 with a cap 3 screwed thereto byscrews 4a,b. In the bearing receiving bore 20 are mounted the upper andlower bearing shells 8, 9 in such a way that the joint faces 11 aresituated in the plane 21 of the cap 3. The shape of the outer and innercontour of the cap 3 after mounting in the bearing receiving bore 20 isillustrated by chain-dotted curves I. After the mounting of the bearing,the cap changed in the vertex 19 and the new inner and outer contour ofthe cap is now described by the curves II. So as to make up for thedimensional variations D of the cap (see FIG. 1), the wall thickness ofthe lower bearing shell 9 is in the vertex 19 correspondingly reduced.The wall thickness of the lower bearing shell 9 decreases continuouslyfrom the joint faces 11 to the vertex 19.

So as to avoid jumps in wall thickness, the wall thickness of the lowerbearing shell 9 in the region of the joint faces 11 is equal to the wallthickness of the upper bearing shell 8 which has a constant wallthickness along the whole circumference.

The crank journal 1, which did not change its position due to thereduced wall thickness of the lower bearing shell 9, lies now on thelower bearing shell without clearance.

The bearing clearance 12 between the upper bearing shell 8 and the crankjournal 1 could remain unchanged. As a consequence of the reduced wallthickness of the lower bearing shell 9 the total outer diameter D_(A) ofboth the bearing shells 8, 9 was reduced by the dimensional variation Dof the cap, whereas the diameter D_(l) of the bearing bore 13 remainedunchanged.

In FIG. 5 is shown a crankcase 5 with a cap 6 attached by screws 7a,b.Also in this embodiment the shape of the cap 6 before and after mountingof the bearing shells 8, 9 and the journal 10 is represented by thecurves I and II. The shapes of the bearing shells 8, 9 correspond tothose described in connection with FIGS. 2 to 4.

In FIG. 6 are shown two bearing shells 8, 9 in unmounted state. Thisembodiment differs from that in FIG. 2 in that on the bearing borehaving the bearing geometry according to the invention is superimposed alemon-shaped bore. The geometry of the lower bearing shell 9 is onlyslightly changed compared to that shown in FIG. 2. The ellipsedescribing the inner contour of the lower bearing shell is preserved,while for the semi-axes applies: a_(i) '<a_(i), b_(i) '>b_(i) and a_(i)'>b_(i) '. The largest change is experienced by the upper bearing shell8 whose wall thickness is now greatest in the vertex 18 and decreasestowards the joint faces 11. In the embodiment illustrated herein thebacking material 22 has a constant thickness and the bearing materialhas a variable thickness. The lemon-shaped bore causes that the innercontour of the upper bearing shell 8 has the shape of a horizontalellipse with a long semi-axis b_(i) ' and a short semi-axis c_(i) '.

Obviously, numerous modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the appended claims,the invention may be practised otherwise than as specifically describedherein.

We claim:
 1. A bearing shell having an outer contour in the shape of acircular arc with a radius r_(a), with a vertex and a pair of joint endfaces, and having a wall thickness which increases from said vertex in acircumferential direction to said joint end faces, such that said shellcomprises an inner contour in the shape of a semi-ellipse with long andshort semi-axes a₁ and b_(i), and wherein the long semi-axis a_(i)passes through said vertex.
 2. The bearing shell according to claim 1,and further comprising a backing material having a constant thicknessalong the whole circumference of said bearing shell and bearing materialdeposited on the backing material with a variable thickness.
 3. Thebearing shell according to claim 1, comprising an outer diameter of 20mm to 1000 mm and wherein the difference in said wall thickness betweenthe wall at said vertex and at said joint faces is up to 0.1 mm.
 4. Aradial plain bearing mounted in a bearing-carrying body provided with abearing cap, the bearing comprising an upper bearing shell and a lowerbearing shell each defining a vertex and a pair of joint faces whereinthe lower bearing shell comprises a wall thickness which increases fromits vertex circumferentially to its joint faces, and the lower bearingshell comprises an inner contour having the shape of a circular arc witha radius r_(i) and an outer contour having the shape of a semi-ellipsewith long and short semi-axes a_(a) and b_(a), and wherein the shortsemi-axis b_(a) passes through the vertex of the lower bearing shell. 5.The radial plain bearing according to claim 4, wherein the outerdiameter of the upper bearing shell and of the inner diameter of thelower bearing shell are centered on a common center point.
 6. The radialplain bearing according to claim 4, wherein the wall thickness of theupper bearing shell and the wall thickness of the lower bearing shell atthe joint faces is the same.
 7. The radial plain bearing according toclaim 4, wherein the wall thickness at the vertex of the upper bearingshell is greater than the wall thickness in the region of the jointfaces.
 8. The radial plain bearing according to claim 4, wherein thebearing shells are each provided with a thrust flange.